Defence Secretary Michael Fallon has made the election campaign personal, accusing Labour leader Ed Miliband of being prepared to “stab the UK in the back” over the UK’s nuclear deterrent.

He said that by striking an electoral deal with the SNP, which is fiercely opposed to Trident renewal, Mr Miliband would show he was prepared to go back on his party’s commitment to adopt the programme.

“Ed Miliband stabbed his own brother in the back to become Labour leader,” Mr Fallon told The Times. “Now he is willing to stab the United Kingdom in the back to become prime minister.”

But is it too late to stop Trident renewal in its tracks? And how much could really be saved by slimming down the amount of equipment used?

£97bn to renew the Trident deterrent

The nuclear deterrent comprises a fleet of four Vanguard submarines carrying up to 64 Trident missiles between them.

Both the submarines and the missiles will need to be replaced in the coming decades.

Renewal is a major election issue because the big decisions need to be taken in the next parliament – on new submarines in 2016 and on a Trident missile replacement in 2019.

Supporters of the current system say four boats are needed to maintain “continuous at-sea deterrence” – an approach which allows the UK to keep one of the submarines at on patrol at all times, with enough back-up to switch submarines as needed and cover unexpected eventualities.

‘Eight Hiroshimas’

That is the estimated destructive power of each Trident missile.

Sixteen missiles can be carried by each of the current Vanguard submarines, all of which can house three warheads.

7,500 miles

The range of each Trident missile, which is accurate to within a few feet.

If one of the missiles was fired from the coast off Brighton, it could reach as far as Chile, South Africa, Indonesia or Japan.